Historically lumber production was a matter of cutting up large diameter logs, producing as many straight boards as could be extracted from the log, with the remainder of the log (a small percentage of the total wood in the log) converted to other uses, e.g., pulp, etc. In recent times, the trees available for cutting are smaller in diameter, e.g., having a 10" diameter as compared to earlier times when the typical log diameter was measured in feet. A slight curve in a 20 foot long, 10 inch diameter log, using the old method of cutting straight lumber pieces would result in perhaps 50% of the log being wasted for lumber purposes.
Present lumber production methods have resolved this waste problem by cutting curved logs along a curved path following the curve of the log. Typically the logs are pre-processed whereby opposed sides are opened to provide opposed flat faces that facilitate control in subsequent operations. Such a pre-processed log is referred to as a cant. Hereafter the description will refer to cants or cant portions and it will be understood that such description encompasses both processed and unprocessed logs. The curved lumber pieces thus extracted from the smaller diameter cants are substantially greater in number than the straight pieces that could be extracted. However, curved sawing presents a number of challenges in the development of machinery that will efficiently produce such curved sawing.
A major problem is the proper feeding of a curved cant into and through the saws. Initially the cant conveying system was developed to feed the cant in a curved path into and through stationary saws. Because the curve changes from cant to cant, the conveyor also had to change the curve of its feeding path. More recent developments that are believed to improve on prior curved sawing techniques allows the cant to be fed along a fixed path with the cutting device, e.g., chipping heads and a bank of saw blades (a saw), being manipulated to follow the curve of the cant. The present invention is directed to this latter type of curved sawing.
In prior straight saw cutting, a cant was scanned to enable a computer to compute the optimum number of straight lumber pieces that could be cut from each cant configuration. The computer determined exactly where the cuts in the cant had to be made and the exact position of the cant on the conveyor. Thus, chipping heads (sometimes referred to as chippers or chipper heads) and saws could be set to cut the cant in accordance with a cutting pattern dictated by the computer. For curved sawing, the computer computes the optimum cutting pattern for the particular curvature of the cant and additionally dictates the curved pathway that the saws have to follow.
In a known system, the cants are conveyed on a fixed linear path. The chippers and saws are mounted on a common support for common pivotal movement but are individually mounted for lateral movement. The chipper heads are small in diameter and the saw blades of the saw are mounted immediately adjacent to and behind the chipping heads. The pivotal axis is between the chipper and saws and as the cants are fed down the fixed conveyor path, the cutting devices are manipulated by the computer and as permitted by the system to follow the curve of the cant.
There are several problems with the above system. Although close together, the commonly mounted, sequentially positioned chipping heads and saw blades are located at a different position along the curve of the cant. Thus there is no pivotal position of the common support that is ideal for both the chipping heads and the saw. The best that can be achieved is to have both the chipping heads and saws slightly offset from the desired curved cutting line. Also, with the chipping heads immediately preceding the saw, chips are thrown directly into the saw blades and disrupt the cutting action of the saw. Also the chipping heads are established at a desired width to open the side faces along the length of the cant. The cants are normally tapered and thus as the smaller end of a cant approaches the chipping heads, one of the chipping heads may be out of contact with the cant side during cutting along the narrow end. The force applied by the opposing chipping head in contact with the cant can force the cant out of its established linear path and as little as 0.030 of an inch of lateral movement of the cant can require reworking of the cant or even loss of a board. Still further, as the faces are opened by the chipping heads, the removal of this material can result in a slight but significant change to the cant's curvature and errors in the cutting process.
The preferred embodiment of the present invention addresses these and other problems with the prior systems.